Elements and rationale for a common approach
to assess and report soil disturbance 1
by Mike Curran2, Doug Maynard3, Ron Heninger4, Tom Terry5,
Steve Howes6, Doug Stone7, Tom NiemannB and Richard E. Millers
ABSTRACT
Soil disturbance from forest practices ranges from barely perceptible to very obvious, and from positive to nil to negative
effects on forest productivity and I or hydrologic function. Currendy, most public and private land holders and various
other interested parties have different approaches to describing this soil disturbance. More uniformity is needed to
describe, monitor, and report soil disturbance from forest practices. We describe required elements for attaining: (1) more
uniform terms for describing soil disturbance; (2) cost-effective techniques for monitoring or assessing soil disturbance;
and (3) reliable methods to rate inherent soil susceptibility to compaction, rutting, mechanical topsoil displacement, and
erosion. Visual disturbance categories are practical for describing soil disturbance. Soil disturbance categories for the
Pacific Northwest are described in detail to illustrate essential elements for attaining Element One. A number of poten­
tial products are listed to meet the other elements. Completion of these will facilitate collecting comparable data and shar­
ing research and training information. Coordinated efforts will also ensure a more seamless process for assessing and
reporting for sustainability protocols, and responding to third-party certification protocols. Additionally, these products
will improve operational relevance of research results.
Key words: soil disturbance, forest productivity, hydrologic function, monitoring, Montreal Process, risk ratings for soils,
soil compaction, soil displacement, soil erosion, sustainability protocols, third-party certification
RESUME
La perturbation du sol au cours des travaux forestiers varie de presque imperceptible a tres evidente, accompagnee d'effets
positifs, nuls et negatifs sur la productivite forestiere ou encore sur les fonctions hydrologiques. Actuellement, la plupart
des proprietaires de terrains publics ou prives, ainsi que les groupes de personnes interessees soutiennent differentes
approches de description de Ia perturbation du sol. Une plus grande uniformite est requise pour decrire, surveiller et faire
etat des perturbations du sol suite a des travaux forestiers. Nous decrivons les elements requis pour obtenir (1) des termes
plus uniformes pour decrire les perturbations du sol, (2) des techniques efficaces en terme de coat pour surveiller ou
evaluer les perturbations du sol et, (3) des methodes fiables pour classer la susceptibilite inherente du sol en terme de
compaction, ornierage, de deplacement mecanique du sol de surface et d'erosion. Les categories visuelles de perturbation
sont utiles pour decrire les perturbations du sol. Les categories de perturbation du sol pour le Nord-Ouest du Pacifique
sont decrites en detail afin d'illustrer les elements essentiels requis pour atteindre le Niveau Un. Plusieurs details
supplementaires sont enumeres dans le cas des autres niveaux. Ces mesures faciliteront la collecte de donnees
comparables et le partage d'information reliee a la recherche et a la formation. Des efforts concertes permettront
egalement d'etablir un processus continu d'evaluation et d'etat de compte dans le cadre des protocoles de durabilite et de
repondre aux protocoles de certification par des tiers. De plus, ces produits accroitront !'importance operationnelle des
resultats de recherche.
Mots des: perturbation du sol, productivite forestiere, fonction hydrologique, surveillance, Processus de Montreal, classes
de risque pour les sols, compaction du sol, deplacement du sol, erosion du sol, protocoles de durabilite, certification par
des tiers
1Cited in our recently published related papers as "A strategy for more uniform assessment and reporting of soil disturbance for operations,
research, and sustainability protocols."
2B.C. Forest Service, Forest Sciences Program, 19 07 Ridgewood Rd., Nelson British Columbia V1L 6Kl. (also, Adjunct Professor,
Agroecology, University of B.C.) Corresponding author. E-mail: mike.curran@gov.bc.ca
3Natural Resources Canada, Canadian Forest Service, 5 06 West Burnside, Victoria, British Columbia V8Z 1M5.
4Weyerhaeuser Company, P.O. Box 275, Springfield, OR, USA 97478-5781.
5Weyerhaeuser Company, Box 42 0, Centralia, WA, USA 98531.
6USDA Forest Service- Pacific Northwest Region P.O. Box 3623, Portland, OR, USA 972 08-3623.
7USDA Forest Service, North Central Research Station, Forestry Sciences Laboratory, 1831 Hwy 169 E, Grand Rapids, MN, USA 55744.
8B.C. Ministry of Forests, Forest Practices Branch, P.O. Box 9513, Stn. Prov. Govt., Victoria, British Columbia V8W 9C2.
9Emeritus Scientist, Pacific Northwest Research Station, Forestry Sciences Laboratory, 3625, 93rd Avenue S.W., Olympia, WA, USA
98512-9193.
852
NOVEMBRE/DECEMBRE 2007, VOL. 83, N° 6 - THE FORESTRY CHRONICLE
log landings, and borrow pits. Many of these may be designed
as permanent structures. Poorly constructed or maintained
forest roads are often the primary source of management­
related sediment on forest lands; road surfaces and ditches
produce sediment that can be delivered to streams if drainage
systems are not properly maintained, and roads in steep ter­
rain can cause landslides if improperly located or constructed
(Furniss et aL 1991). In addition, the landbase dedicated to
the access network is not available to grow trees or forage. For
these reasons, most public jurisdictions not only have limits
on the amount of permanent access but also prescribe con­
struction and maintenance best practices. Other temporary
roads, landings, and even logging trails may be part of the
access network during active harvesting of an area but these
are subsequently restored to hydrologically stable conditions,
and preferably ameliorated to a productive condition.
While definitions of access networks may be reasonably
similar amongst jurisdictions, differences exist for how road
areas are measured and what limits for percent coverage are
set. T here may be reasons for having different limits (e.g., ter­
rain constraints); however, it is desirable that limits be applied
to the same unit of measure, most commonly the gross har­
vested area of a cutblock (activity area). It is also desirable to
have a similar approach to other aspects of access manage­
ment, as provided below.
Provisional disturbance definitions for access road networks
Permanent access may include roads, landings, and borrow
pits, and any harvesting or yarding trails that will be fre­
quently used or that are permanent. Permanent access typi­
cally ·is considered a permanent loss from the productive
landbase and may require tracking under international sus­
tainability protocols or third-party certification standards for
wood products. To compare area occupied by roads, we need
common protocols for width measurement because berms
and sidecasts typically feather off over considerable distance
(e.g., 20-cm fill depth is used in B.C. as per Fig. 1).
Temporary access includes roads, landings, or trails that
are not needed until the next rotation. Temporary access is
often rehabilitated and reforested to restore hydrologic
function and soil productivity.
Rehabilitated roads are increasingly an operational objec­
tive to reduce maintenance costs and risk of stream sedi­
mentation. Criteria should be established to judge com­
pleted (successful) mitigation.
•
•
Dispersed (in-block) disturbance
Some internal access is required within a given cutblock being
harvested or site prepared, prescribed burned, or managed as
rangeland. T his access may include parts of the permanent
road network that will be required for other activities nearby or
for repeated entry activities like grazing or partial-cut harvest­
ing. 'In addition, temporary access may be required for thin­
ning, or other mechanical operations. In the example of har­
vesting, a very small or large amount of the harvested area may
be disturbed depending on the method of harvest, site condi­
tions, and access constraints. Helicopter or skyline harvesting
may result in minor gouging and scalping of the surfuce soil.
Cable or grapple yarding may result in deeper gouging on some
yarding corridors, and ground-based harvesting may create soil
rutting, compaction, and displacement from heavy equipment
operating on trails or elsewhere across the site.
854
It is difficult to relate specific soil disturbance at the time
of an activity like harvesting to long-term hydrologic and
productivity consequences. This is because our knowledge
base is incomplete and climatic events, revegetation, natural
amelioration, and site conditions vary tremendously.
However, there is a need to manage and minimize the poten­
tial for negative effects. Monitoring the severity and extent of
soil disturbance at the time of harvest can be used to track
progress towards this goal, but it is critical to have data to val­
idate which disturbance classes actually impact hydrologic
function, productivity, or other ecosystem functions of con­
cern.
In many jurisdictions, regulation of in-block soil distur­
bance is based on quantified changes in soil properties and I
or visually identifiable categories of disturbance. These sys­
tems are based on best available information, ranging from
peer-reviewed research to expert and practitioner opinion.
Visual systems usually have specified conditions that must be
met before a disturbance "counts" towards a cumulative total
within the area to be reforested. To reduce uncertainty, visual
systems and" counted" disturbance classes should be validated
by research that relates visual observed conditions to soil
property thresholds and forest productivity and hydrologic
function within given soil and climatic areas.
Following development since the 1980s in B.C., machine
traffic and displacement disturbance types have been defined
primarily on visual characteristics and dimensions (Fig. 1 and
Table 1) (B.C. Ministry of Forests 2001). These definitions
were embodied in regulation under the Forest Practices Code
Act in 1995; however, hardwiring definitions in legislation
does little to encourage their evolution over time.
Consequently, the new Forest and Range Practices Act refers to
them as well, but in a way that provides for their revision over
time based on research and scientific literature. The threshold
conditions (e.g., dimensions) at which disturbance types are
counted as detrimental are based on assessing site-specific
susceptibility ratings for compaction, displacement, or ero­
sion at that location. This counted disturbance is considered
potentially detrimental to tree growth or site hydrology. To
prevent anticipated negative effects, allowable area for this
dispersed, counted disturbance is limited by some jurisdic­
tions. In B.C., this currently ranges from So/o of the activity
area on sensitive soils to lOo/o on less-sensitive soils.
Weyerhaeuser Company (Scott 2000, as referenced in
Heninger et aL 2002) has developed and used another visual
approach to classify soil disturbance (Fig. 2). The classifica­
tion system is based on the ty pe and degree of disturbance
(compaction, puddling, and displacement) to topsoil and
subsoil in traffic lanes caused by machine traffic. A similar
system tested on the Wallowa-Whitman National Forest
includes more displacement definitions and only four traffic
disturbance classes. This enables focus on the more severe dis­
turbance classes considered "counted" (Table 2).
In other Canadian provinces and internationally, ruts
appear to be the most common disturbance type recognized
by various agencies and researchers; however, a number of
provinces (e.g., Alberta, Saskatchewan, and Ontario) are cur­
rently reviewing their approaches to soil disturbance. Some
jurisdictions set critical threshold levels for various soil prop­
erties (Powers et aL 1998). For example, criteria for com­
paction focus on absolute or relative changes in bulk density,
porosity, or soil strength. One concern with these measure-
NOVEMBRE/DECEMBRE 2007, VOL. 83, N° 6 - THE FORESTRY CHRONICLE
Table 1. Soil disturbance definitions from the previous B.C. Forest Practice Code Act, Operational Planning Regulations• (still in
use today and abbreviated for this paper with clarification provided in [square brackets]).
Compacted area- an area of soil that [requires rehabilitation]:
is greater than 1 00m2 in area and greater than 5 m wide;
(a) has a moderate, high or very high soil compaction hazardb or the assessment of its soil compaction hazard was not done (b )
[such as cable-harvested areas]; has been compacted by equipment travelling over it, and;
(c) (d) has one or more of the following attributes:
(i) altered soil structure or increased density relative to the surrounding undisturbed soil,
(ii) soil puddling,
(iii) compacted deposits of forest floor, fine slash I woody debris overlaying or crushed into the mineral soil.
Dispersed disturbance
-
areas of soil occupied by dispersed trails, gouges and scalps.
Excavated or bladed trail- constructed trail that has [requires rehabilitation]:
an excavated or bladed width greater than 1.5 m, and;
(a) (b) mineral soil cutbank height greater than 30 em
.
Dispersed trail - an area that is not a compacted area but that, due to equipment traffic on the soil, has the following attributes:
impressions or ruts in the soil that are at least:
(a) (i) 30 em wide, 2 m long and a minimum of 15 em deep where depth is measured from the surface of the undisturbed forest
floor to the deepest point in the cross-section over the entire length of 2m, or,
(b) (ii) if the area has a high or very high soil compaction hazard, 30 em wide, 2m long and a minimum of 5 em deep where depth
is measured from the surface of the undisturbed mineral soil to the deepest point in the cross-section over the entire length
of 2 m;
has the same attributes as Compacted Area (d) on an area of soil at least 1 m X 2m that has a moderate, high or very high soil
compaction hazard.
Gouge- an excavation into the mineral soil that is:
deeper than 30 em;
(a) (b) deeper than 5 em where it covers:
(i) at least 80o/o of a 1.8 m X 1.8 m area, or
(ii) an area of at least 1 m X 3 m, or;
(c) to the depth of the underlying bedrock.
Scalp - an area in which the forest floor has been removed from:
(a) over 80o/o of a 3 m X 3 m area or:
(i) over 80o/o of a 1.8 m X 1.8 m area if the area,
(ii) has a very high soil displacement hazard,
(iii) has a very high soil compaction hazard or soil erosion hazard.
•The general
BCFS Web site where these and other FPC or FRPA information can be located is http://www.for.gov.bc.cal
hHazard refers to the susceptibility or vulnerability of the soil to undergo significant compaction.
inconsistent application of standards and muddled public
perceptions. Soil specialists may thoroughly assess soil condi­
tions within proposed activity areas before prescribing soil
management objectives, but application of this information is
ineffective when contract administrators and operators lack
the understanding and ability to identify disturbance cate­
gories. Consequently, undesirable soil conditions often result
from misunderstandings or miscommunication, or from a
lack of training.
Government agencies also must deal with disparate
groups having different perceptions about soil disturbance
and its effects on productivity and ecosystem functions. The
likelihood of effectively resolving potentially adversarial situ­
ations will increase if all participants use the same terms and
definitions, and there is sound research to support the recom­
mendations.
Uniform definitions and procedures for describing, mon­
itoring, and reporting disturbances would also assist commu-
856 nication across jurisdictions. Efficiency of limited budgets
and resources for soil disturbance assessments, research, and
extension could all be improved by sharing the development
of training materials, brochures, monitoring protocols, and
the research that supports these products. National and inter­
national reporting, such as under the Montreal Process crite­
ria and indicators, would be more consistent and improve
understanding of each member nation's efforts to improve
soil management and conservation.
What disturbance is detrimental?
Not all soil disturbances are detrimental. One general defini­
tion of soil disturbance is "any disturbance that changes the
physical, chemical, or biological properties of the soil" (Lewis
et al. 1991). Note that the direction or consequences of these
changes are not specified. Site preparation is commonly pre­
scribed for planting and establishing seedlings. Disturbance
related to these activities is usually not considered detrimen­
NOI/EMBRE/cECfMBRE 2007 VOL. 83 N" 6
o
o
-
THE FORESTRY CHRONICLE
Table 2. Interim severity classes for soil disturbance in the Wallowa-Whitman National Forest (Modified from USFS 2001 I
Oass 0: Undisturbed Natural State
Soil resistance to penetration with tile spade or probe:
Soil surface:
•
No evidence of past equipment operation.
•
No depressions or wheel tracks evident.
•
Litter and duff layers present and intact.
•
No soil displacement evident.
Observations of soil physical conditions:
•
•
Oass 1: Low Soil Disturbance
·
•
•
Faint wheel tracks or slight depressions evident and are
<6 inches deep.
Soil surface:
Surface soil has not been displaced and shows minimal
mixing with subsoil.
•
Resistance of surface soils may be slightly greater than
observed under natural conditions. Concentrated in top
0-4 inch depth.
Litter and duff layers are missing.
•
Evidence of topsoil removal, gouging and piling.
•
Change in soil structure from crumb or granular struc­
ture to massive or platy structure, restricted to the sur­
face 0-4 inches.
•
•
Wheel tracks or depressions are >6 inches deep
.
Litter and duff layers partially intact or missing.
•
Surface soil partially intact and may be mixed with
subsoil.
The objective of most management strategies is to limit
the amount of detrimental soil disturbance and prevent
cumulative detrimental effects. Ultimately, management
strategies-whether thresholds for unacceptable disturbance
or best management practices-should be based on actual,
confirmed effects on tree growth, site hydrology, and other
resource values. Similarly, national and international report­
ing, such as under the Montreal Process' new indicator 4.2.b,
"Area and percent of forest land with significant soil degrada­
tion" (Montreal Process Working Group 2006), should be
based on consideration of these site-dependent effects, and
not simply on uniform application of specified thresholds for
degraded soil density or organic matter content, since these
may or may not "count" as detrimental to soil functions and
productivity. More specifically, validated, site-specific criteria
are needed for defining soil degradation or hydrologic func­
tion disruption rather than using generalized criteria, such as
percent change in soil density or organic matter content,
since these changes would likely affect soil functions and
productivity differently across a range of sites.
Recommendations: Review existing soil disturbance classifica­
tions. Decide on common themes and simple categories that
are operationally relevant and convenient for reporting results.
Develop uniform definitions or descriptions to facilitate
858 .
Increased resistance is deep into the soil profile (> 12
inches).
Observations of soil physical conditions:
Soil surface:
•
Soil displacement has removed the majority of the
surface soil. Surface soil may be mixed with subsoil.
Subsoil partially or totally exposed.
Soil resistance to penetration with tile spade or probe:
Class 2: Moderate Disturbance
•
Wheel tracks or depressions highly evident with depth
being> 12 inches deep.
•
Observations of soil physical conditions:
•
Platy structure is generally continuous.
Class 3: High Disturbance
Litter and duff layers present and intact.
Soil resistance to penetration with tile spade or probe:
•
Change in soil structure from crumb or granular struc­
ture to massive or platy structure, restricted to the sur­
face 4-12 inches.
Large roots may penetrate the platy structure, but fine
and medium roots may not.
Soil surface:
•
Increased resistance is present throughout top 4-12
inches of soil.
Change in soil structure from granular structure to
massive or platy structure extends beyond the top 12
inches of soil.
Platy structure is continuous.
Roots do not penetrate the platy structure.
meaningful comparisons and learning from well-planned
research studies and soil-disturbance monitoring. Suggested
requirements for common definitional terms include cate­
gories for required (permanent) access, as discussed above,
and for dispersed disturbance that meet the following criteria:
Types and severity of disturbance are dearly defined and
effects on off-site soil movement, site productivity, or
hydrology are under test or validated using a research­
quality strategic database.
Categories span the range of soil disturbance likely to
occur with current and future forest practices.
Disturbance category definitions can be understood and
easily recognized by laypersons (i.e., categories are dear
and unambiguous).
Disturbance categories are visually discernible and readily
recognized by equipment operators in the field.
Distinctions are made among soil/climate types when
determining those disturbance categories that are
"counted" (detrimental) and those that are not.
Consistent definitions are provided for both permanent and temporary access, and for acceptable rehabilitated dis­
turbance. It is recognized that what is considered detrimental will vary depending on the site conditions. Technical committees
currently operating or proposed for regional, national, and
•
•
•
•
•
•
NOVEMBAE/
Cl:MBRE 2007, VOL. 83, N° 6 - THE FORESTRY CHRONICLE
mate of the parameter in question (e.g., small bias and rea­
sonable precision), and strike a balance between cost and
enforceability.
The total amount of soil disturbance in an activity area can
be composed of many small polygons, a few large polygons,
or, more commonly, a combination of these two extremes.
Therefore, pattern and distribution of disturbance should be
documented in monitoring reports. Areas of soil disturbance
can remain undetected when the survey area is large and sam-.
piing intensity is low. It is possible to stratify areas based on
the susceptibility of soils to detrimental disturbance (e.g.,
region, soil type, climate zone). One solution is to allocate the
highest proportion of quantitative or detailed disturbance
monitoring in areas with sensitive soils, but it is important
that all strata have some sampling intensity to assess the entire
activity area.
Sampling intensity
Desired levels of confidence and acceptable uncertainty in
statistical estimates must be set before establishing sampling
intensity. These will depend on the decisions being made
from the data and on the risks deemed acceptable by those
conducting (requiring or approving) the survey. In addition,
one should consider the consequences of making a wrong
decision (based on the sampling data). More precise informa­
tion may be needed (hence a larger sample size) if. (1) a deci­
sion is to be made about contract violation or rule infraction,
(2) information is to be used in court proceedings, (3) envi­
ronmental consequences are potentially severe, or (4) effects
of new equipment are being evaluated. In contrast, less pre­
cise information may suffice for: (1) assessing performance
relative to broad standards and guidelines, (2) internal evalu­
ations of operations or planning for restoration, or (3) envi­
ronmental consequences are inconsequential. Sample sizes
are always dependent on how precisely one needs to estimate
the mean, the population variability, and the level of confi­
dence one desires. But with any sampling design, there is a
point at which the marginal benefits (increased accuracy or
precision) do not out-weigh the marginal costs of sampling.
Weyerhaeuser's sampling intensity was developed from
several field trials where a predetermined acceptable margin
of error was set. For compliance or enforcement monitoring
decisions, surveys are required to specify confidence limits
and levels. For example, if survey data indicate that 18% of
the cutblock was detrimentally disturbed, does this exceed the
15% standard? In British Columbia, the 90% confidence limit
is used for compliance (B.C. Ministry of Forests 2001). If the
mean and 90% confidence limits were 18 ± 5% in our exam­
ple, then a standard of 15% was not exceeded because the
lower confidence limit would be 13%.11 This is consistent
with a statement by McMahon (1995), in his summary of a
study of two survey methods on small areas: " ... where single
(sic; non-replicated) surveys are being used to assess site dis­
turbance, it is necessary to recognize the inherent variability
in estimated results. This is particularly important when
using the assessment results to determine compliance with a
quantitative standard."
11In this case a one-sided confidence interval also may be appropri­
ate to calculate if one wants to know with known confidence that
the population mean is either at least or no larger than some com­
puted number (Siegel 2 003).
860
To avoid the expense of formal surveys, informal methods
can produce rapid evaluations of active operations or for an
overview assessment at final harvest inspection. Informal sur­
veys may provide the screening basis for recommending or
requiring formal surveys. Several protocols have been devel­
oped for visual walk- through estimation of disturbance; these
often involve pacing or hip-chaining along transects to esti­
mate average coverage and to locate concentrations of distur­
bance. In the past, these methods have been considered to
provide acceptable levels of precision for this task; however,
computation of confidence intervals is not appropriate for
informal assessments. With the widespread availability of
electronic maps, photos, and GPS, some of this field checking
will likely be replaced by more random walkthrough assess­
ments (to discrete GPS points) or remote sensing- based
assessments. In BC, informal methods are used on hundreds
of cutblocks annually and have been incorporated into the
Soil Resource Stewardship Monitoring Protocol for B.C.
(Province of B.C. 2005).
What is recorded?
Some protocols document all soil disturbances, while others
count only disturbances that are deemed detrimental. To
ensure comparability of results, documenting all disturbance
categories is preferable. This allows for maximum use of the
data for comparisons as well as for tracking beneficial distur­
bance. Moreover, counted disturbance can be derived when
the consequences of disturbance types is known or assessed
through longer-term research studies.
Which disturbance is "counted" varies gready across juris­
dictions, pardy in response to regional differences in soil
resistance and resilience, and how various guidelines evolved.
Operational staff in the Pacific Northwest Region (USPS)
have struggled to determine what patterns of disturbance
(size and shape) should be considered "detrimental" to soil
productivity when conducting assessment surveys. Currently,
there is a minimal or threshold size limitation for counting
soil displacement as detrimental (i.e., 9.3 square meters and
1.5 meters wide). It is most important to assess disturbance
classes known or expected to be detrimental based on the
information available. Current guidelines for this USPS
Region state that no more than 20% of an activity area may
have soil in "detrimental" disturbance classes, including per­
manent and temporary access roads (USPS 1998). Each
Region of the Forest Service has developed its own policy and
standards that can be found in various locations within their
directives system. One consideration would be to indicate
which disturbance types are confirmed to be detrimental and
which are tentative until validated by research.
Current B.C. guidelines (standards) limit permanent
access roads and landings to 7% on a cutblock basis. In-block
limits for counted soil disturbance were defined under the
previous Forest Practices Code and these definitions still
apply for the new Forest and Range Practices Act. Two main
types of disturbance are recognized: machine tracks and dis­
placement. The definitions of these disturbance types are
summarized in Table 1, with diagrams in Fig. 1. Machine
tracks include excavated and bladed trails (skid roads), and
disturbance from skidding logs. Excavated and bladed trails
(skid roads) are considered temporary access that must be
rehabilitated and their area, in combination with that of dis­
persed disturbance (displacement), must not exceed a speci­
NOVEMBRE/cECEMBRE 2007, VOL. 83, N° 6 - THE FORESTRY CHRONICLE
Table 3. Hazard key for soil compaction and puddling (B.C. Ministries of Forests and Environment 1995)
Hazard Rating'>
moisture regime
Xeric-subhygricf
Subhygric-subhydricl
(0-30 em)
(H horizons <20 em)
(H horizons 01::20 em)
Fragmental Coarse fragments> 7 0%
L
M
Sandy
S, LS
L
Sandy Loam
SL, fSL
M
Soil TextureA
< 7 0%
Coarse
Fragments
Silty/Loamy
SiL, Si, L
Clayey
SCL, CL, SiCL,
SC, SiC, C
VHe
H
VH
'Use dominant soil texture and coarse fragment content of the upper 30 em of mineral soil to assess compaaion hazard. If a pronounced textural change occurs within the upper 30 em (e.g., silty over sandy soil), then use the more limiting soil texture, providing it amounts to 5 em of the top 30 em. bL = Low; M = Moderate; H =High; VH =Very High. 'Use this column for subhygric sites with forest floor H-horiwns < 20 em thick. duse this column for subhygric sites with forest floor H-horizons:.: 20 em thick. 'Organic soils composed of more than 40 em of wet organic material or forest floors> 40 em (including Folisols < 40 em) are susceptible to rutting due to their very low load­
bearing strength materials. Consequently, these organic materials have a high soil displacement hazard and a very high soil compaaion and puddling hazard. The B.C. key does not consider moisture status of the site or
depth of surface soil (depth to dense subsoil), because wet soil
conditions occur on all sites in some period each year, and
most soils in B.C. have dense subsoils close to the surface. This
approach may be too simple for other regions where soils
remain moist much of the year or where no winter season
enables low-impact harvest. In application, hazard (suscepti­
bility) ratings need to be tempered with consideration of on­
site moisture conditions by the logging supervisor or equip­
ment operator.
Textural classes, as defined by the Canadian System of Soil
Classification (Day 1983) or the USDA-NRCS are weak indi­
cators of soil resistance to mechanical stress. There are at least
two problems with using textural classes. First, in textural
analysis, it is not uncommon that some of the soil minerals
influencing in-situ behaviour are removed from the sample
before texture determination (e.g., organic matter, calcareous
material, iron and aluminum oxides). Second, some texture
classes have a very large range in clay content (e.g., 0 to 28o/o
for silt loam). Some clay-size mirierals respond differently to
mechanical forces, exhibiting different cohesive properties
like plasticity and stickiness. Therefore, to predict soil behav­
iour, we need to supplement soil textural classes.
Soil consistence (degree of cohesion and adhesion) as
defined in the Canadian System of Soil Classification
(Day1983) provides useful interpretations for harvest plan­
nirig in relation to addressing risk of soil compaction (Curran
1999, Curran et al. 2000). Moreover, a test group of college
students more accurately and consistently estimated moist
consistence (plasticity) than textural classes. As expected,
"plastic" soils varied in actual clay content, presumably
because their clay minerals differ. Content of sand and silt
also affected plasticity. Siltier soils were plastic at clay contents
as low as 12o/o (Curran, unpublished data). Although use of
86 2
soil consistence classes currently does not change soil com­
paction ratings, it alerts users to soil conditions that are more
likely to lead to compaction and rutting. Fig. 3 relates plastic­
ity to the texture triangle (note that silt loam encompasses
three plasticity classes).
Tree performance and compaction
Excessive soil compaction and puddling are of particular con­
cern in timber-harvesting operations because of their imme­
diate effects on soil properties and roots of residual trees and
subsequent effects on regeneration and tree growth.
Compacted soils may impede root growth due to greater pen­
etration resistance, lower aeration porosity, and slower rates
of infiltration and hydraulic conductivity. Aeration porosity is
a reliable indicator of compaction. Lowered aeration porosity
reduces gas exchange, which in turn affects oxygen and car­
bon dioxide concentrations in the soil; this may reduce phys­
iologic functions of roots and lead to root mortality during
wet conditions. Compacted soils remain wet longer. This can
reduce seedling growth due to lower soil temperature and
poorer aeration under some conditions.
In coarse-textured soils, compaction may increase water­
holding capacity and increase tree growth (Powers and
Fiddler 1997, Stone et aL 1999, Gomez et aL 2002, Ares et al.
2005). Coarse-textured soils typically have lower compaction­
hazard (risk) ratings. Tree growth on rehabilitated landings
(Bulmer and Curran 1999, Plotnikoff et al. 1999) and haul­
roads (Curran, unpublished) demonstrate that sandier soils
appear repairable following compaction. Finer textured soils
typically have higher compaction-risk ratings, but may be
amendable to rehabilitation. For example, tree growth on
rehabilitated skid trails on silty clay loams in the Oregon
Cascades was not different from trees on undisturbed soil
(Heninger et al. 2002). Other textures require further study.
NOVEMBRE/oECl:MBRE 2007, VOL. 83, N° 6 - THE FORESTRY CJ-IRONICtE
not uncommon for the forest floor to contain over 50o/o of the
total soil nitrogen and 80o/o of the phosphorus. Because many
B.C. forest sites are nitrogen-deficient, conservation of the
forest floor is important. Curran et aL (1990) developed a
process for rating forest floor displacement susceptibility to
be used when planning harvest and site preparation opera­
tions in B.C.
Soil factors affecting both forest floor and topsoil displace­
ment risk include depth of fertile soil materials, mineral soil
texture and coarse fragments, slope, and topography. Topsoil
displacement is the lateral movement of mineral soil caused
by moving equipment and logs and is recognized in soil dis­
turbance classifications in B.C. (Fig. 1), the various classifica­
tions of the USDA Forest Service (e.g., Table 2), and in DC3
and DC4 of the Weyerhaeuser disturbance classification sys­
tem (Fig. 2). Displacement includes excavation, scalping,
exposure of underlying materials, and burial of more fertile
surface soils.
Three effects of displacement can compromise soil pro­
ductivity and site hydrology: (1) exposure of unfavourable
subsoils (dense, gravelly, or calcareous soil with high pH); (2)
redistribution and loss of nutrients; and (3) alteration of
slope hydrology, which can lead to the hydrologic effects dis­
cussed previously with compaction. In addition, exposure of
mineral soil can lead to erosion and displacement of fertile
topsoil on steep slopes and is more prevalent with certain soil
textures and geologic I topographic formations. This is the
subject of watershed analyses and erosion ratings that are not
discussed here.
Topsoil depth is the key indicator of topsoil-displacement
risk as used by Weyerhaeuser's risk-rating system. In more
northern temperate forests, the soils that have developed on
glaciated terrain are often shallow. In these and other forests
throughout the world, many nutrients are concentrated in the
forest floor and the top 20 em of mineral soil. Therefore,
managers need to avoid displacing fertile topsoil too far from
seedlings, and maintain the volume of topsoil available for
rooting. The presence of unfavourable subsoils or water tables
also warrants a high risk rating. Under other climatic condi­
tions and with older soils, soil displacement is of more or less
concern, depending on total soil depth and the characteristics
of the subsoil. For example, detrimental productivity or
hydrologic function changes are more likely on a soil with a
shallow A horizon (e.g., 2-cm depth) and a high water table
than one with a very deep A horizon (e.g., 40 em) enriched in
organic matter without a perched water table.
Tree performance and forest floor/soil displacement
We need better understanding of the effects of organic matter
removals, the role of coarse woody debris, and the impacts of
site preparation (tillage and/or vegetation control) on long­
term site productivity (Stone et al. 1999, Fleming et al. 2006).
Increasing intensity of organic matter removal decreased
both diameter and height growth of aspen on sandy soils in
the Lake States region of the U.S.A. Stone et aL (1999).
Displacement of topsoil has reduced tree growth when high
pH subsoils are exposed (Smith and Wass 1979), and when
rooting volume is largely restricted to subsoils of poor fertil­
ity or limited moisture-holding capacity (Clayton et aL 1987).
Currently, more studies are yielding further information
including the LTSP (Powers et aL 2005) and some
86 4
university/industry/agency collaborative studies (Kelting et
aL 2000, Ares et aL 2007).
Recommendations: Existing methods for risk rating soils should
be reviewed, and reliable methods and criteria identified.
Although soils can be mapped at a variety of scales and with
a variety of objectives, we encourage detailed soil mapping
( 1:24 000 scale or larger) and representative descriptive data
for each mapping unit. Soils mapped in the USA as part of the
National Cooperative Soil Surveys are mapped at the land
type or land type-phase level of a hierarchy of ecological
units; map scale is usually 1:24 000. This is the level at which
most direct soil risk-rating methods have been developed.
One still needs on-site inspection to confirm accuracy of the
mapping and hence the actual soil series to be rated. In the
absence of detailed soil mapping, each area proposed for
harvest requires its own soil assessment as part of harvest
planning, which is the procedure used in B.C. (Curran et aL
2000). Other bases for soil risk rating should be considered.
Burger and Kelting (1998), for example, noted a clear rela­
tionship between Least-Limiting Water Range (LLWR) and
productivity on various disturbance types. This characteristic
should be evaluated for a range of soils. Further research is war­
ranted on both LLWR and moist-soil consistency (plasticity).
We currently have methods for risk rating soils as to their
likelihood for being negatively impacted by equipment traf­
fic. We should now further test their validity by measuring the
effects of operational practices on soil characteristics and,
ultimately, on productivity and hydrologic function. Results
of this validation monitoring may warrant changes in rating
systems and guidelines.
Summary and Final Recommendations
We discussed and recommended development of more
uniform and effective: (1) soil disturbance categories and
their relationship to productivity; (2) monitoring protocols
that facilitate comparison and transportability of operational
and research results within and across geographic regions and
jurisdictions; (3) ratings of soils for risk of compaction, rut­
ting, and displacement.
To support this initiative, a wealth of completed and cur­
rent work needs synthesis. Products and deliverables include:
State-of-the-art reviews and position papers about soil
disturbance categories, alternative monitoring methods,
and risk-rating systems.
Common definitions of potentially detrimental soil dis­
turbance types for specified areas based on reviews of
hydrologic and tree response to soil disturbance.
Coordinated training and extension materials for forest
workers and lay persons.
Effective methods for converting operational and research
information into periodically updated soil management
guidelines and BMPs.
Common soil disturbance guidelines for similar soils and
climate.
Continued involvement with forest certification and sus­
tainability protocols to ensure their operational relevance.
These products and actions will not only promote collec­
tion of more comparable data by states, provinces, USFS
regions, and private ownerships, but also ensure a more
seamless process for reporting at national and international
•
•
•
•
•
•
NOIIEMBRE/
Cl:MBRE 2007, VOL. 83, N° 6 - THE FORESTRY CHRONICLE
Douglas-fir on nontilled and tilled skid trails in the Oregon
Cascades. Can. ]. For. Res. 32: 233-246.
Howes, S.W., J.W. Hazard and J.M. Geist. 1983. Guidelines for sam­
pling.some physical conditions of surface soils. USDA Forest Service.
Pacific Northwest Region. R6-RWM- 146- 1983.
Kelting, D.L, J.A. Burger and S.C. Patterson. 2000 . Early loblolly
pine growth response to changes in the soil environment New
Zealand Journal of Forest Science 30(1/2): 206-224.
Kuennen, L, G. Edson and T.V. Tolle. l 979. Soil compaction due to
timber harvesting activities. Soil, Air, and Water Notes 79-3. USDA
Forest Service, Northern Region.
Lewis, T. and Timber Harvesting Subcommittee. 1 99 1 . Developing
timber harvesting prescriptions to minimize site degradation. B.C.
Min. Forests Land Management Report No. 62.
Lock, B.A. 2001 . Measuring the degree of impact on the ground - an
indicator approach (Website talk from In-Woods Ground
Disturbance Workshop, Truro, Nova Scotia, Canada. Nov. 7-8, 200 1
[online] . Available at http://www.feric.ca/en/ed/htmVproceedings
.htm [accessed March 1 7, 2005 ] .
McMahon, S . 1 995. Accuracy o f two ground survey methods for
assessing site disturbance. Journal of Forest Engineering 6: 27-33.
Miller, R.E., W. Scott and J.W. Hazard. 1 996. Soil disturbance and
conifer growth after tractor yarding at three coastal Washington
locations. Can. J. For. Res. 26: 225-236.
Montreal Process. 1 999. Criteria and indicators for the conservation
and management of temperate and boreal forests. The Montreal
Process Liaison Office. Available at http://www. mpci.org.
Montreal Process Working Group. 2006 1 7th Meeting of the
Working Group. Annex F: Summary table of the revised indicators
approved by the Working Group at its 1 7th meeting. Available at
http://www.mpci.org.
Partington, M., J. Lirette and M. Ryans. 2005. Using GPS to manage
partial-cutting operations in tolerant hardwoods. Advantage. Vol. 6
No. 29. 4 p.
Plotnikoff, M., M. Schmidt, C. Bulmer and M. Curran. 1 999 . Forest
productivity and soil conditions on rehabilitated landings: Interior
British Columbia. B.C. Min. Forests, Research Branch, Extension
Note 40.
Powers, R.F. 2006. Long-Term Soil Productivity: genesis of the con­
cept and principles behind the program. Can. J. For. Res. 36:
5 1 9-528.
Powers, R.F. and G.O. Fiddler. 1997. The North American Long­
Term Soil Productivity Study: progress through the first 5 years. In
Proceedings, Eighteenth Annual Forest Vegetation Management
Conf., Jan. 1 4-16, 1997. Sacramento, CA. Published by the Forest
Vegetation Management Conference, Redding, CA.
Powers, R.F., A.E. Tiarks and J R. Boyle. 1 998. Assessing soil quality:
Practicable standards for sustainable forest productivity in the
United States. In: E.A. Davidson et aL (eds.). The contribution of
soils science to the development of and implementation of criteria
and indicators of sustainable forest management. pp. 53-80. SSSA
Pub!. 53. Soil Science Society of America, Madison, WI.
.
.
866
Powers, R.F., D.A. Scott, F.G. Sanchez, R.A. Voldseth, D. Page­
Durnroese and J.D. Elioff. 2005. The North American Long-term
Soil Productivity Experiment. Findings from the first decade of
research. For. Ecol. Manage. 220: 3 1-50.
Province of British Columbia. 2005. Protocol for soil resource stew­
ardship monitoring: Cutblock level. (Curran, Mike, Chuck Bulmer
and Shannon Berch, compilers, with other contributors noted on the
first page). FRPA Resource Evaluation Program, B.C. Ministry of
Forests, B.C. Min. Water, Land and Air Protection, and B.C. Ministry
Sustainable Resource Management., Victoria, B.C. 42 p. Available at:
http://www.for.gov.bc.calhfp/frep/7_rsm.html.
Scott, W. 2000. A soil disturbance classification system. Internal
Report For. Res. Tech. Note, Paper #00- 1 . Weyerhaeuser Co., Federal
Way, WA. 12 p.
Siegel, A.F. 2003. Practical Business Statistics (Fourth Edition). Irwin
McGraw-Hill.
Smith, R.B. and E.F. Wass. 1976. Soil disturbance, vegetative cover
and regeneration on clearcuts in the Nelson Forest District, British
Columbia. Fisheries and Environment Canada, Can. For. Serv.,
Inform. Rep. BC-X- 1 5 1 .
Smith, R.B. an d E.F. Wass. 1 979. Tree growth o n and adjacent to
contour skid roads in the subalpine zone, southeastern British
Columbia. Can. For. Serv., Pacific Forestry Center, Info. Report BC­
R-2. 26 p.
Stone, D.M. 2001 . Sustaining aspen productivity in the Lake States.
In W.D. Shepperd, D. Binkley, D.L. Bartos, T.J. Stohlgren, and L.G.
Eskew ( comps.). Sustaining aspen in western landscapes:
Symposium Proceedings. pp. 47-59. USDA For. Service Rocky
Mountain Res. Stn. Proc. RMR-P- 18.
Stone, D.M. and J.D. Elioff. 2000. Soil disturbance and aspen regen­
eration on clay soils: three case histories. For. Chron. 76: 747-752.
Stone, D.M., J.A. Gates and J.D. Elioff. 1999. Are we maintaining
aspen productivity on sand soils? In B. ZumBahlen and A.R. Ek
(romps.). Improving Forest Productivity For Timber - A Key to
Sustainability, Proceedings of Conference, 1-3 December 1 998,
Duluth, MN. pp. 1 77-1 84. Department of Forest Resources,
University of Minnesota, St. Paul, MN.
Terry, T. and R.G. Campbell. 1981. Soil management considerations in
intensive forest management. In Forest Regeneration. Proceedings of
the Agriposium on Engineering Systems for Forest Regeneration,
March 2-6, 198 I . pp. 98- 108. Am. Soc. Agric. Engineers, St. Joseph, MI.
USFS. 1998. USDA Forest Service Manual, FSM 2520 (Watershed
Protection and Management) R-6 Supplement No. 2500-98 - 1 ,
Effective August 24, 1 998.
USFS. 200 1 . Interim protocol for assessments and management of
soil quality conditions, Wallowa-Whitman National Forest. Mimeo,
Version 3.3, September 200 1 . USDA Forest Service, Wallowa­
Whitman National Forest.
Wass, E.F. and J.P. Senyk. 1 999. Tree growth for 15 years following
stumping in interior British Columbia. Technology Transfer Note
No. 1 3, April 1 999. Natural Resources Canada, Canadian Forest
Service, Pacific Forestry Centre, Victoria BC.
NOVEMBRE/
Cl:MBRE 2007, VOL. 83, N° 6 - THE FORESTRY CHRONICLE